The present invention generally relates to a continuous, non-tower process for producing a particulate detergent composition. More particularly, the invention is directed to a continuous process where a free-flowing dry neutralized detergent powder is agglomerated with a liquid or viscous paste binder to form agglomerates. The process produces detergent agglomerate having a reduced amount of fine particles and over-sized particles that require recycle.
Recently, there has been considerable interest within the detergent industry for laundry detergents which are xe2x80x9ccompactxe2x80x9d and therefore, have low dosage volumes. To facilitate production of these so-called low dosage detergents, many attempts have been made to produce high bulk density detergents, for example with a density of 500-600 g/l or higher. The low dosage detergents are currently in high demand as they conserve resources and can be sold in small packages which are more convenient for consumers. However, the extent to which modern detergent products need to be xe2x80x9ccompactxe2x80x9d in nature remains unsettled. In fact, many consumers, especially in developing countries, continue to prefer a higher dosage levels in their respective laundering operations.
Generally, there are two primary types of processes by which detergent granules or powders can be prepared. The first type of process involves spray-drying an aqueous detergent slurry in a spray-drying tower to produce highly porous detergent granules (e.g., tower process for low density detergent compositions). In the second type of process, the various detergent components are dry mixed after which they are agglomerated with a binder such as a nonionic or anionic surfactant, to produce high density detergent compositions (e.g., agglomeration process for high density detergent compositions). In the above two processes, the important factors which govern the density of the resulting detergent granules are the shape, porosity and particle size distribution of said granules, the density of the various starting materials, the shape of the various starting materials, and their respective chemical composition.
There have been many attempts in the art for providing processes which increase the density of detergent granules or powders. Particular attention has been given to densification of spray-dried granules by post tower treatment. The following references are directed to densifying spray-dried granules: Appel et al, U.S. Pat. No. 5,133,924 (Lever); Appel et al, U.S. Pat. No. 5,164,108 (Lever); Bortolotti et al, U.S. Pat. No. 5,160,657 (Lever); Johnson et al, British patent No. 1,517,713 (Unilever); and Curtis, European Patent Application 451,894. As an example, one attempt involves a batch process in which spray-dried or granulated detergent powders containing sodium tripolyphosphate and sodium sulfate are densified and spheronized in a Marumerizer(copyright). This apparatus comprises a substantially horizontal, roughened, rotatable table positioned within and at the base of a substantially vertical, smooth walled cylinder. This process, however, is essentially a batch process and is therefore less suitable for the large scale production of detergent powders. More recently, other attempts have been made to provide continuous processes for increasing the density of xe2x80x9cpost-towerxe2x80x9d or spray dried detergent granules. Typically, such processes require a first apparatus which pulverizes or grinds the granules and a second apparatus which increases the density of the pulverized granules by agglomeration. The stochastic nature of most pulverizing and agglomeration processes often results in the undesired broadening of particle size distributions, resulting in both fine dusty particles and coarse oversize particles; this requires additional corrective process steps such as screening, elutriation, grinding and recycling in order to meet desired product specifications for particle size. As such, treating or densifying by xe2x80x9cpost towerxe2x80x9d is not favorable in terms of economics (high capital cost) and complexity of operation. Moreover, all of the aforementioned processes are directed primarily for densifying or otherwise processing spray dried granules. In addition, products made by treating or densifying xe2x80x9cpost towerxe2x80x9d or spray dried granules, in absence of other post-process steps such as spray-on coating, are typically limited in their ability to go higher in surfactant active level because of limitations inherent to the spray-drying process. Currently, the relative amounts and types of materials subjected to spray drying processes in the production of detergent granules has been limited For example, it has been difficult to attain high levels of surfactant in the resulting, detergent composition, a feature which facilitates production of detergents in a more efficient manner. Thus, it would be desirable to have a process by which detergent compositions can be produced without having the limitations imposed by conventional spray drying techniques.
To that end, the art is also replete with disclosures of processes which entail agglomerating detergent compositions. For example, attempts have been made to agglomerate detergent builders by mixing zeolite and/or layered silicates in a mixer to form free flowing agglomerates. Mixer/agglomerator processes can deliver high product throughputs; however, these products are typically either broad in their particle size distribution (i.e., they include dusty fines and coarse oversize) or they rely on substantial classification and recycle loops (e.g., recycle rate greater than 20% by weight of the production rate) to maintain a desired particle size distribution. See for example U.S. Pat. No. 5,516,448.
The following references are directed to producing detergents by agglomeration: Beujean et al, Laid-open No. WO93/23,523 (Henkel), Lutz et al, U.S. Pat. No. 4,992,079 (FMC Corporation); Porasik et at, U.S. Pat. No. 4,427,417 (Korex); Beerse et al, U.S. Pat. No. 5,108,646 (Procter and Gamble); Capeci et at, U.S. Pat. No. 5,366,652 (Procter and Gamble); Hollingsworth et at, European Patent Application 351,937 (Unilever); Swatling et at, U.S. Pat. No. 5,205,958; Dhalewadikar et at, Laid Open No. WO96/04359 (Unileaver). For example, the Laid-open No. WO93/23,523 (Henkel) describes the process comprising pre-agglomeration by a low speed mixer and further agglomeration step by high speed mixer for obtaining high density detergent composition with less than 25 wt % of the granules having a diameter over 2 mm. The U.S. Pat. No. 4,427,417 (Korex) describes continuous process for agglomeration which reduces caking and oversized agglomerates.
On the other hand, examples of processes to make detergent products with narrow particle size distributions by an extrusion/spheronization process are also known. However, these products are typically limited to particle sizes of about 1000 micron and above, and typically do not achieve throughput rates that are as high as mixer/agglomerator processes. While such attempts suggest that their process can be used to produce detergent agglomerates, they do not provide a mechanism by which starting detergent materials in the form of pastes, liquids and dry materials can be effectively agglomerated into crisp, free flowing detergent agglomerates, where the detergent product is characterized by i) high active level of chemical surfactants (i.e., generally more than 15 weight %), ii) particle size distribution of the agglomerates with a geometric mean particle size in the range between 250 to 1200 microns and a geometric standard deviation of less than 2.5, and iii) high bulk density (i.e., greater than 500 g/l); and by a detergent making process having a high throughput (i.e., greater than 1 metric ton/hour) continuous process, where the process is efficient by virtue of its minimal reliance of recycle streams (i.e., less than 20 weight % of the product rate) for product that is either too fine (e.g., less than 250 microns) or too coarse (e.g., greater than 1400 microns) in particle size.
Accordingly, there remains a need in the art to have a non-tower process for continuously producing a detergent composition delivered directly from starting detergent ingredients, where the density of the resulting detergent composition can be achieved by adjusting the process condition. Also, there remains a need for such a process which is more efficient, flexible and economical to facilitate large-scale production of detergents (1) for flexibility in the ultimate density and particle size of the final composition, (2) for incorporating high levels of detergent surfactant into the final composition, and (3) for flexibility in terms of incorporating several different kinds of detergent ingredients (especially liquid ingredients) into the process.
The present invention provides a continuous process for preparing a granular detergent agglomerate having a density of at least about 500 g/l, comprising the steps of:
(a) in a first step, dispersing and mixing a liquid acid precursor of an anionic surfactant with a solid particulate water-soluble alkaline material in a high speed mixer for a mean residence time of about 0.2 to about 50 seconds, wherein the acid precursor is partly or totally neutralized, thereby forming a dry neutralized material comprising a salt of the anionic surfactant precursor in the form of a free-flowing powder; and
(b) in a second step, dispersing and mixing an agglomeration binder with the free-flowing powder in a moderate speed mixer, thereby of agglomerating the powder into granular detergent agglomerates.
The present invention produces high density detergent agglomerates for use in granular detergent compositions, having a high level of detergent surfactant and a relatively narrow particle size distribution. Furthermore, the process is inherently efficient by significantly reducing the amount of agglomerate which is outside an acceptable particle range. The present invention also meets the aforementioned needs in the art by providing a process which produces a granular detergent composition for flexibility in the ultimate density of the final composition from an agglomeration (e.g., non-tower) process. The process does not require the use of conventional spray drying towers which have limited capability to produce compositions having a high surfactant loading (concentration) at high bulk density (greater than 500 gm/l).
Accordingly, it is an object of the invention to provide a process for continuously producing a detergent composition which has flexibility with respect to bulk density, size, size distribution, chemical composition and surfactant active level of the final products by controlling residence time, mixing element tip speed and binder dispersion conditions in the mixers. It is also an object of the invention to provide a process which is more efficient, flexible and economical to facilitate large-scale production.
The process described herein provides a granular detergent agglomerate having a high density of at least about 500 g/l and relatively narrow particle size distribution as measured by the geometric standard deviation of less than about 2.5, with high throughput capability and increased production efficiency, and with less recycle of material having an unacceptable particle size. While it is recognized that other processes which include classification and recycle loops are capable of producing more narrow particle size distributions measured at the final product output, the advantage of the current invention is the narrowness of the particle size distribution before any classification is done.